To determine the frequency and significance of mitral anular calcium (MAC) in hypertrophic cardiomyopathy (HC), 43 clinical and morphologic variables in 194 necropsy cases of HC were examined. Of 96 patients less than or equal to 40 years of age, none had MAC. Of the 98 necropsy patients greater than 40 years of age, 30 (31%) had MAC, and of them 21 (70%) were women. The mean age of the 30 MAC patients was older than that of the 68 non-MAC patients greater than 40 years of age (66 years-vs-54 years). The frequency of MAC increased with age.